Chemometric analysis of carbon-13 NMR chemical shifts of 13 classes of aliphatic organic compounds bearing halogens are reported. The effects of F, Cl, Br, and I were explored using principal component analysis (PCA) starting from a matrix formed from experimental (NMR) data and theoretically obtained physical-chemical properties (Gaussian 98). The PCA results, applying three principal components and three variables for data description, divided the alpha-substituent effects on the carbon-13 chemical shifts of the compounds analyzed into four-classes. These directly depend on heteroatom type (halogen). The four-class separation occurred as a consequence of partial charge alterations of the alpha-carbon atom (PC1) and its molecular orbital coefficients (PC2). (C) 2004 Elsevier B.V. All rights reserved.681416994749